Most of the nutritionally significant biological nitrogen fixation is carried out by Rhizobia/Bradyrhizobia, bacteria that fix nitrogen only within the nodules they form on the roots of legumes. Our long-term goal is to improve the efficiency of fixation and to broaden the host range to nonlegumes. The research proposed here is to understand the initial interaction between the host an the symbiont and how the plant utilizes the reduced nitrogen. The proposal focuses on two major aspects: (i) to determine the role of flavonoids in nodule initiation; (ii) to determine if ammonia assimilation can be improved and if that would have an impact on the overall N-status of the plant. For the first part of our project, the focus is on genes encoding for key enzymes in the phenylpropanoid pathway leading to flavonoid synthesis - phenylalanine ammonia lyase (PAL), chalcone synthase (CHS) and chalcone isomerase (CHI). The study involves studying the regulation of the different members of the family and the effect of over/under expressing key members, on nodule initiation. Glutamine synthetase (GS), the key enzyme in ammonia assimilation, is central to our understanding of ammonia assimilation and is the theme of the second part. Our research combines a molecular and biochemical approach to understand the functional role and regulatory mechanism underlying expression of different GS gene members. Furthermore, the effect of down and up regulation of different GS gene members on the efficiency of ammonia assimilation and N2-fixation, is being studied. A second project aimed towards improving the nutritional quality of legume seeds and forage, that is being pursued in the lab, is to introduce into these plants highly expressing genes encoding for high sulfur amino acid proteins. Altogether, the projects in the lab utilize state-of-the-art techniques in molecular biology, biochemistry and cell biology to address important issues in plant biology that have a direct impact on human nutrition.